Allow access to full logs in Harbormaster builds

Harbormaster helpfully tries building every commit and every differential revision. However, when it fails, we only get the tail of the output, with no way to get more information.

A case in point is this build, where a performance test case failed with [stat too good]. In this particular case, the commit is intended to be an optimization, so this failure is not terribly unexpected. I wanted to update all.T with the new figure, but I couldn't get the figure that Harbormaster's configuration had. Instead, I had to run the test on my machine (a Mac), get a different number, and hope that Harbormaster's configuration fell within 5% of mine. It did, in this case, but might not next time.